The present invention relates to an earth leakage breaker having a function of protecting a circuit of a low-voltage power distribution system against over-current and ground failure. More particularly, the present invention relates to an earth leakage breaker having protective means for disconnecting an earth-leakage-detection circuit from a main power distribution circuit when a dielectric-strength test is conducted.
As a conventional device for protecting a low-voltage power distribution system, a circuit breaker and an earth leakage breaker have been well known. An earth leakage breaker currently available has a function of protecting against over-current and ground failure. A conventional earth leakage breaker, for example, as disclosed in Japanese Patent No. 3246562, has a configuration in which a circuit breaker or an earth leakage breaker on an identical frame is retained in a main-body case with an identical size and common main components are used, so that it is convenient to use.
Further, as disclosed in Japanese Patent No. 3097368, a circuit breaker or an earth leakage breaker is provided with various attachments such as an auxiliary switch, an alarm switch, a voltage tripping coil, a short-voltage tripping coil, and the like, so that the circuit breaker or the earth leakage breaker can be applicable to a wide variety of protecting systems for a power distribution system.
A circuit diagram of a conventional earth leakage breaker (for a 3-phase circuit) is shown in FIG. 12, and a structure thereof is shown in FIG. 13. In FIG. 12, the reference numeral 1 designates a main circuit comprising phases R, S, and T. The reference numeral 2 designates main contacts. The reference numeral 3 designates a switch mechanism of the main contact 2. The reference numeral 4 designates an operating handle. The reference numeral 5 designates a thermal or electro-magnetic over-current tripping device for detecting an over-current or short-circuit current so that the switch mechanism performs a tripping operation.
A leakage tripping device detects ground failure in a power distribution system, so that the switch mechanism performs a tripping operation. The leakage tripping device comprises a zero-phase current transformer 6 for detecting an unbalanced current in the main circuit 1 with the main circuit 1 of the R-S-T-phase as a primary conductor; an earth-leakage-detection circuit 7 (electronic circuit including an IC) for detecting the ground failure according to a secondary output level of the zero-phase current transformer 6; and a tripping-coil unit 8 for causing the switch mechanism to perform the tripping operation upon reception of an output signal from the earth-leakage-detection circuit 7.
Inter-phase voltage of the main circuit 1 is supplied to the earth-leakage-detection circuit 7 as a power source thereof via a power-supply line 9 and a rectifying circuit 10 disposed between the main circuit 1 and the earth-leakage-detection circuit 7. In FIG. 12, inter-phase voltage between the R-T phases of the main circuit 1 is supplied to the earth-leakage-detection circuit 7. Voltage at the R-T-S phases may be converted to DC voltage, and the DC voltage is supplied to the earth-leakage-detection circuit 7.
As shown in FIG. 13, the reference numeral 11 designates a main-body case partitioned into two parts, i.e. a lower case portion 11a and an upper cover portion 11b. The reference numerals 12 and 13 designate main-circuit terminals (screw terminals) at a side of a power source and a side of a load, respectively. The reference numeral 14 designates a stationary contact connected to the main-circuit terminal 12. The reference numeral 15 designates a movable contact. The reference numeral 16 designates a rotary contact holder for supporting the movable contact 15. The reference numeral 17 designates an arc extinction unit.
The switch mechanism 3 comprises an assembly of a toggle-link mechanism comprising a toggle link 3a interconnecting the contact holder 16 and the operating handle 4 and an opening/closing spring 3b ; and a latching mechanism comprising a latch unit 18, a latch receiver 19, and a tripping cross bar 20. The tripping cross bar 20 faces the over-current tripping device 5 and an operating end portion of the tripping-coil unit 8 (shown in FIG. 12). The latching mechanism shown in FIG. 13 is an example, and there are other latching mechanism structures.
As shown in FIG. 14, the main-body case 11 is provided with partitions 11c for dividing components of each of the phases mounted in the main-body case 11. The leakage detecting circuit 7 is mounted on a print board 7a, and installed inside the main-body case 11 (space between the zero-phase current transformer 6 and a side wall of the main-body case 11). The power supply line 9 (refer to FIG. 12) is connected between the leakage detecting circuits 7 and conductors of the main circuit 1. In the main-body case 11, there are disposed a lead wire corresponding to the over-current tripping device 5 disposed in series to each phase of the main circuit 1, lead wires connecting a secondary output side of the zero-phase current transformer 6 and the earth-leakage-detection circuit 7, and lead wires connecting the earth-leakage-detection circuit 7 and the tripping-coil unit 8.
In the above constitution, when the operating handle 4 is moved between ON/OFF positions, the toggle-link mechanism of the switch mechanism 3 is operated along with the operating handle 4, thereby opening and closing the movable contact 15. In a state that the main contacts are closed (ON) as shown FIG. 13, the latch unit 18 engages the latch receiver 19, and the tripping cross bar 20 supports the latch receiver 19 at this position. When an over-current or short-circuit current flows in the main circuit 1 under the above condition, the over-current tripping device 5 is activated, so that the tripping cross bar 20 rotates counterclockwise to release the latch receiver 19 from the latch unit 18. Accordingly, the switch mechanism 3 performs a tripping operation to separate the movable contact 15 from the stationary contact 14, thereby shutting off the current flowing through the main circuit 1.
When the ground-failure current flows through the main circuit 1, the tripping-coil unit 8 of the leakage tripping device is activated, so that the tripping cross bar 20 moves to a release position. Accordingly, the switch mechanism 3 performs the tripping operation to open the movable contact 15, thereby shutting off the current flowing through the main circuit 1. After the tripping operation, the operating handle 4 is returned to RESET position from the tripping position (slightly beyond OFF position) to reset the latching mechanism, and the operating handle 4 is moved from the OFF position to the ON position to close the movable contact 15, so that the breaker is activated again.
For the safety reason, the earth leakage breakers need to meet dielectric strength requirements according to the industry standard. Accordingly, an individual product is subject to a test to confirm that the product meets the requirements. According to a test method specified by the industry standard, specific voltage is applied between the phases of the main-circuit terminals. The specific voltage depends on a rated voltage of the earth leakage breaker, for example, a test voltage of 2,500 V is applied to an earth leakage breaker with the rated voltage of 300 V to 600 V.
In Japan, it is customary that a manufacturer conducts the dielectric-strength test before shipment of the product. In this case, if high voltage is applied between the phases while the earth-leakage-detection circuit (IC) is connected to the main circuit in the assembled state of the earth leakage breaker, the high voltage damages the earth-leakage-detection circuit. For this reason, the dielectric-strength test is conducted after the power lines of the earth-leakage-detection circuit are disconnected.
On the other hand, unlike the practice in Japan, in Europe and the U.S., a circuit breaker is provided with an earth-leakage-detection unit (unit of a zero-phase current transformer and an earth-leakage-detection circuit) as a separated unit. Accordingly, a service person conducts the dielectric-strength test in a state that the earth-leakage-detection unit is attached to the circuit breaker. In order to conduct the dielectric-strength test, U.S. patent publication No. 2001/0022713A1 has disclosed an earth-leakage-detection unit provided with a push-button-type switch for the dielectric-strength test. When the dielectric-strength test is conducted, the switch is operated to disconnect the earth-leakage-detection circuit from the main circuit. After the test, the switch is operated to connect the earth-leakage-detection circuit to the main circuit, thereby restoring a normal use condition.
The conventional earth leakage breakers have the following disadvantages with respect to the dielectric-strength test. As shown in FIG. 13, the earth leakage breaker is assembled in the main-body case in which the leakage tripping device including the components of the circuit breaker and the earth-leakage-detection circuit is installed. Accordingly, when the dielectric-strength test is conducted, it is necessary to remove an external cover of the main-body case, and disconnect the earth-leakage-detection circuit from the main circuit by removing soldered portions or screwed portions of the power-supply lines between the earth-leakage-detection circuit and the main circuit, thereby requiring a large amount of work.
In the earth-leakage-detection device disclosed in U.S. Patent Publication No. 2001/0022713A1, it is arranged such that when the switch provided in the earth-leakage-detection unit is turned OFF to conduct the dielectric-strength test, the earth-leakage-detection circuit is disconnected from the main circuit and the circuit breaker performs the tripping operation to open the main contact. Accordingly, it is possible to safely conduct the dielectric-strength test by disconnecting the earth-leakage-detection circuit from the main circuit.
However, the operation of the switch is not linked to the opening/closing operation of the circuit breaker, and the switch can be operated independently to restore the ON state. Therefore, after the dielectric-strength test, even when the switch is not returned to the ON status, it is possible to manually operate a handle provided in the circuit breaker to turn on the main contacts. Accordingly, an operator may forget to return the switch to the ON status after the dielectric-strength test, and the operator manually operates the handle provided in the circuit breaker to turn on the main contacts, so that the circuit breaker returns to an operable status. In this case, the earth-leakage-detection circuit remains disconnected from the main circuit. As a result, when the ground failure occurs in the circuit breaker in the operable state, the protective function against the leakage does not work.
Further, the earth leakage breaker has an outer dimension same as that of the circuit breaker. As shown in FIG. 14, the components for over-current protection and leakage protection are arranged inside the main-body case with no space, and there is no sufficient room for disposing an additional switch for the test. Therefore, in order to provide a space for the switch for the test in the main-body case, it is necessary to change a design of the components and a layout thereof. It takes a large amount of cost and time to change the common components in the circuit breaker and the earth leakage breaker, and the layout thereof.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide an earth leakage breaker comprising components of a circuit breaker, an earth-leakage-detection circuit, and an over-current tripping device assembled in a single body case as shown in FIG. 13. In the earth leakage breaker, it is possible to disconnect the earth-leakage-detection circuit from the main circuit via a simple operation, so that the dielectric-strength test is safely conducted after shipment of a product.
Another object of the present invention is to provide an earth leakage breaker in which a test switch is added in a space of a main-body case without significantly changing components and a layout of the earth leakage breaker, so that the dielectric-strength test is safely conducted after shipment of a product.
Further object and advantages of the invention will be apparent from the following description of the invention.